Pattern generator using a dual phase step element and method of using same

ABSTRACT

A system and method are used to pattern light using an illumination system, an array of individually controllable components, and a projection system. The illumination system supplies a beam of radiation. The array of individually controllable elements patterns the beam. The array of individually controllable elements comprises mirrors having first and second steps on opposite edges. The projection system projects the patterned beam onto a target portion of an object. In various examples, the object can be a display, a semiconductor substrate or wafer, a flat panel display glass substrate, or the like, as is discussed in more detail below.

BACKGROUND

1. Field of the Invention

The present invention relates to a light patterning device and method ofusing same.

2. Related Art

A patterning device is used to pattern incoming light. A staticpatterning device can include reticles or masks. A dynamic patterningdevice can include an array of individually controllable elements thatgenerate a pattern through receipt of analog or digital signals. Exampleenvironments for use of the patterning device can be, but are notlimited to, a lithographic apparatus, a projector, a projection displayapparatus, or the like.

When imaging with micromirror arrays as the object, the phase of thelight reflected by each mirror is critical. For example, when a flattilting mirror is untilted (e.g., resting) light at the image planeand/or collected at projection optics is considered to have on averagezero phase, i.e., has positive amplitude. During tilting of the mirror,there is an tilt angle at which no light on average is directed towardthe image plane and/or is collected at projection optics, so the averageamplitude of the light at the image plane goes to zero. Then, as themirror continues to tilt, out of phase light reaches the image planeand/or is collected at projection optics, which is considered to benegative amplitude light. In conventional arrays of individuallycontrollable elements having tilting mirrors, a maximum amount ofnegative light reaching the image plane is much smaller (e.g., of lowerintensity or amplitude) than a maximum amount of positive light reachingthe image plane.

When imaging with tilting mirrors, there can be a telecentricity error.Telecentricity can occur during patterning on an object as a patterngoes into and out of focus, and causes an image being formed tomove/shift.

Currently, arrays of individually controllable elements can includevarious types of mirrors. Mirror types include, but are not limited to,flat tilting mirrors, single phase-step tilting mirrors, piston mirrors,or hybrid mirrors combining tilt and piston actions. However, because ofintensity modulation constraints (e.g., unequal maximum amplitude ofpositive and negative light) these arrays cannot effectively emulatephase shifting masks and/or are inefficient when correcting telecentricerrors. Individually, piston mirrors have a pure phase modulationeffect, but amplitude modulation can also be obtained by combiningpiston mirrors into superpixels. A superpixel is formed when groups ofpixels (e.g., 2×2, 4×4, or 8×8, etc) are combined to create one largepixel. This superpixel can collect increased amounts of light. Thisincreases sensitivity (e.g., speed), but can sacrifice resolution. Thesesuperpixels can then behave as graytone pixels with the capability ofachieving an intensity modulation anywhere between 100% positive phaseintensity and −100% negative phase intensity. There are, however, asdiscussed above, limitations in replicating the effect of assistfeatures smaller than the superpixel.

Another alternative, also discussed above, is a single phase-steptilting mirror (λ/4 height step and phase step of λ/2, where λ is animaging wavelength), for example, by Micronic Laser Systems of Sweden.This mirror can achieve an intensity modulation anywhere between +50%and −50%. When at rest, no light enters a pupil of a projection systembecause, due to the step, half the light has a zero degree phase and theother half of the light has a 180 degree phase. As the mirror is tilted,light is captured or collected by the projection system, where adirection of tilt determines whether positive or negative light iscaptured or collected. Because of the symmetry of the single stepmirror, equal amounts of positive and negative light can be captured orcollected by the projection system. However, to correct for telecentricerrors, the one step mirror requires alternating the position of thestep (right or left), which is discussed below. This results in thedependence of the tilt angle sign on the position of the edge. Thismeans that in order to achieve a given graytone with a particularmirror, the sign of the tilt angle needed requires knowledge of wherethe step is located, which creates an additional strain on the datapath. In addition, mirror curling at the edges is likely to beexacerbated on a thinner side of the mirror and result in “tilt errors.”

Therefore, what is needed is an array of individually controllableelements, where each individually controllable element when used in thearray has better positive and negative intensity characteristics and/orallows for effective and efficient telecentric error correction.

SUMMARY

According to one embodiment of the present invention, there is provideda system comprising an illumination system, an array of individuallycontrollable elements, and a projection system. The illumination systemsupplies a beam of radiation. The array of individually controllableelements patterns the beam. The array of individually controllableelements comprises mirrors having first and second steps on oppositeedges. The projection system projects the patterned beam onto a targetportion of an object.

According to one embodiment of the present invention, there is provideda patterning device comprising an array of first reflecting components,an array of second reflecting components, and an array of controllers.Each of the first reflective components has a first width and a firstlength. Respective ones of the array of second reflective components arecoupled to a central portion of respective ones of the array of firstreflective components. Each of the second reflective components has asecond width, which is substantially equal to the first width, and asecond length, which is smaller than the first length. First steps areformed between first edges of respective ones of the coupled togetherfirst and second reflective components. Second steps are formed betweensecond edges of respective ones of the coupled together first and secondreflective components. The array of controllers are coupled torespective ones of the coupled together first and second reflectivecomponents. Each of the controllers controls the movement of each of therespective ones of the coupled together first and second reflectivecomponents.

According to another embodiment of the present invention, there isprovided a patterning device comprising a first and second array ofreflective components and an array of controllers. The array of firstreflective components each have a first width and a first length.Respective ones of the array of second reflective components are coupledto a peripheral portion of respective ones of the array of firstreflective components. Each of the second reflective components have asecond width, which is substantially equal to the first width, and asecond length, which is smaller than the first length. First steps areformed between first edges of respective ones of the coupled togetherfirst and second reflective components and second steps are formedbetween second edges of respective ones of the coupled together firstand second reflective components. The array of controllers is coupled torespective ones of the coupled together first and second reflectivecomponents. Each of the controllers control the movement of each of therespective ones of the coupled together first and second reflectivecomponents.

According to another embodiment of the present invention, there isprovided a device manufacturing method comprising the following steps.Patterning a beam of radiation using an array of individuallycontrollable elements, each element in the array having first and secondsteps on opposite edges. Projecting the patterned beam onto a targetportion of an object.

Further embodiments, features, and advantages of the present inventions,as well as the structure and operation of the various embodiments of thepresent invention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate embodiments of the present inventionand, together with the description, further serve to explain theprinciples of the invention and to enable a person skilled in thepertinent art to make and use the invention.

FIG. 1 depicts a lithographic apparatus, according to one embodiment ofthe invention.

FIG. 2 depicts a patterning device, according to one embodiment of theinvention.

FIGS. 3 and 4 depict a top and side view, respectively, of an element ina patterning device, according to one embodiment of the presentinvention.

FIGS. 5 and 6 are graphs depicting reflectivity over a range of tiltangles of different sized elements in a patterning device, according toembodiments of the present invention.

FIG. 7 shows a two dimensional diffraction pattern for a dual phase stepelement in a patterning device, according to embodiments of the presentinvention.

FIG. 8 depicts a side view of an element in a patterning device,according to one embodiment of the present invention.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers mayindicate identical or functionally similar elements.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Overview

Although specific reference may be made in this text to the use of apatterning device in a lithographic system that patterns a substrate, itshould be understood that the patterning device described herein mayhave other applications, such as in a projector or a projection systemto pattern an object or display device (e.g., in a projection televisionsystem, or the like). Therefore, the use of the lithographic systemand/or substrate throughout this description is only to describe exampleembodiments of the present invention.

A system and method are used to pattern light using an illuminationsystem, an array of individually controllable devices, and a projectionsystem. The illumination system supplies a beam of radiation. The arrayof individually controllable elements patterns the beam. The array ofindividually controllable elements comprises mirrors having first andsecond steps on opposite edges. The projection system projects thepatterned beam onto a target portion of an object. In various examples,the object can be a display device, a semiconductor substrate or wafer,a flat panel display glass substrate, or the like, as is discussed inmore detail below.

The dual-step element provides an increased range of modulation ofintensity compared to conventional systems. The dual-step element alsoprovides substantially equal positive and negative maximum amplitudes,which allows for sharper images to be formed by an array of individuallycontrollable dual-step elements at an image plane in which the object islocated.

Terminology

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as, for example, the manufacture of DNA chips,MEMS, MOEMS, integrated optical systems, guidance and detection patternsfor magnetic domain memories, flat panel displays, thin film magneticheads, micro and macro fluidic devices, etc. The skilled artisan willappreciate that, in the context of such alternative applications, anyuse of the terms “wafer” or “die” herein may be considered as synonymouswith the more general terms “substrate” or “target portion,”respectively.

The substrate referred to herein may be processed, before or afterexposure, in, for example, a track (a tool that typically applies alayer of resist to a substrate and develops the exposed resist) or ametrology or inspection tool. Where applicable, the disclosure hereinmaybe applied to such and other substrate processing tools. Further, thesubstrate may be processed more than once, for example, in order tocreate a multi-layer IC, so that the term substrate used herein may alsorefer to a substrate that already contains multiple processed layers.

The term “array of individually controllable elements” as here employedshould be broadly interpreted as referring to any device that can beused to endow an incoming radiation beam with a patterned cross-section,so that a desired pattern can be created in a target portion of thesubstrate. The terms “light valve” and “Spatial Light Modulator” (SLM)can also be used in this context. Examples of such patterning devicesare discussed above and below.

A programmable mirror array may comprise a matrix-addressable surfacehaving a viscoelastic (i.e., a surface having appreciable and conjointviscous and elastic properties) control layer and a reflective surface.The basic principle behind such an apparatus is that, for example,addressed areas of the reflective surface reflect incident light asdiffracted light, whereas unaddressed areas reflect incident light asundiffracted light. The addressing can be binary or through multipleintermittent angles. Using an appropriate spatial filter, theundiffracted light can be filtered out of the reflected beam, leavingonly the diffracted light to reach the substrate. In this manner, thebeam becomes patterned according to the addressing pattern of thematrix-addressable surface.

It will be appreciated that, as an alternative, the filter may filterout the diffracted light, leaving the undiffracted light to reach thesubstrate. An array of diffractive optical micro electrical mechanicalsystem (MEMS) devices can also be used in a corresponding manner. Eachdiffractive optical MEMS device can include a plurality of reflectiveribbons that can be deformed relative to one another to form a gratingthat reflects incident light as diffracted light. This is sometimesreferred to as a grating light valve.

A further alternative embodiment can include a programmable mirror arrayemploying a matrix arrangement of tiny mirrors, each of which can beindividually tilted about an axis by applying a suitable localizedelectric field, or by employing piezoelectric actuation means. Onceagain, the mirrors are matrix-addressable, such that addressed mirrorswill reflect an incoming radiation beam in a different direction tounaddressed mirrors; in this manner, the reflected beam is patternedaccording to the addressing pattern of the matrix-addressable mirrors.The required matrix addressing can be performed using suitableelectronic means. In one example, groups of the mirrors can becoordinated together to be addresses as a single “pixel.” In thisexample, an optical element in a illumination system can form beams oflight, such that each beam falls on a respective group of mirrors.

In both of the situations described here above, the array ofindividually controllable elements can comprise one or more programmablemirror arrays.

A programmable LCD array can also be used.

It should be appreciated that where pre-biasing of features, opticalproximity correction features, phase variation techniques and multipleexposure techniques are used, for example, the pattern “displayed” onthe array of individually controllable elements may differ substantiallyfrom the pattern eventually transferred to a layer of or on thesubstrate. Similarly, the pattern eventually generated on the substratemay not correspond to the pattern formed at any one instant on the arrayof individually controllable elements. This may be the case in anarrangement in which the eventual pattern formed on each part of thesubstrate is built up over a given period of time or a given number ofexposures during which the pattern on the array of individuallycontrollable elements and/or the relative position of the substratechanges.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.,having a wavelength of 365, 248, 193, 157 or 126 nm) and extremeultra-violet (EUV) radiation (e.g., having a wavelength in the range of5-20 nm), as well as particle beams, such as ion beams or electronbeams.

In the lithography environment, the term “projection system” used hereinshould be broadly interpreted as encompassing various types ofprojection systems, including refractive optical systems, reflectiveoptical systems, and catadioptric optical systems, as appropriate, forexample, for the exposure radiation being used, or for other factorssuch as the use of an immersion fluid or the use of a vacuum. Any use ofthe term “lens” herein may be considered as synonymous with the moregeneral term “projection system.”

The illumination system may also encompass various types of opticalcomponents, including refractive, reflective, and catadioptric opticalcomponents for directing, shaping, or controlling the beam of radiation,and such components may also be referred to below, collectively orsingularly, as a “lens.”

The lithographic apparatus maybe of a type having two (e.g., dual stage)or more substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

The lithographic apparatus may also be of a type wherein the substrateis immersed in a liquid having a relatively high refractive index (e.g.,water), so as to fill a space between the final element of theprojection system and the substrate. Immersion liquids may also beapplied to other spaces in the lithographic apparatus, for example,between the substrate and the first element of the projection system.Immersion techniques are well known in the art for increasing thenumerical aperture of projection systems.

Further, the apparatus may be provided with a fluid processing cell toallow interactions between a fluid and irradiated parts of the substrate(e.g., to selectively attach chemicals to the substrate or toselectively modify the surface structure of the substrate).

Exemplary Environment for a Patterning Device

Although the patterning device of the present invention can be used inmany different environments, as discussed above, a lithographicenvironment will be used in the description below. This is forillustrative purposes only.

A lithographic apparatus is a machine that applies a desired patternonto a target portion of an object. The lithographic apparatus can beused, for example, to pattern an object in a biotechnology environment,in the manufacture of ICs, flat panel displays, micro or nano fluidicdevices, and other devices involving fine structures. In a an IC-basedlithographic environment, the patterning device is used to generate acircuit pattern corresponding to an individual layer of the IC (or otherdevice), and this pattern can be imaged onto a target portion (e.g.,comprising part of one or several dies) on a substrate (e.g., a siliconwafer or glass plate) that has a layer of radiation-sensitive material(e.g., resist). As discussed above, instead of a mask, in maskless IClithography the patterning device may comprise an array of individuallycontrollable elements that generate the circuit pattern.

In general, a single substrate will contain a network of adjacent targetportions that are successively exposed. Known lithographic apparatusinclude steppers, in which each target portion is irradiated by exposingan entire pattern onto the target portion in one go, and scanners, inwhich each target portion is irradiated by scanning the pattern throughthe beam in a given direction (the “scanning” direction), whilesynchronously scanning the substrate parallel or anti-parallel to thisdirection. These concepts will be discussed in more detail below.

FIG. 1 schematically depicts a lithographic projection apparatus 100,according to one embodiment of the invention. Apparatus 100 includes atleast a radiation system 102, a patterning device 104 (e.g., a staticdevice or an array of individually controllable elements), an objecttable 106 (e.g., a substrate table), and a projection system (“lens”)108.

Radiation system 102 is used to supply a beam 110 of radiation, which inthis example also comprises a radiation source 112.

Array of individually controllable elements 104 (e.g., a programmablemirror array) is used to pattern beam 110. In one example, the positionof the array of individually controllable elements 104 is fixed relativeto projection system 108. However, in another example, array ofindividually controllable elements 104 is connected to a positioningdevice (not shown) that positions it with respect to projection system108. In the example shown, each element in the array of individuallycontrollable elements 104 are of a reflective type (e.g., have areflective array of individually controllable elements).

Object table 106 is provided with an object holder (not specificallyshown) for holding an object 114 (e.g., a resist coated silicon wafer, aglass substrate, or the like). In one example, substrate table 106 isconnected to a positioning device 116 for accurately positioningsubstrate 114 with respect to projection system 108.

Projection system 108 (e.g., a quartz and/or CaF2 lens system or acatadioptric system comprising lens elements made from such materials,or a mirror system) is used to project the patterned beam received froma beam splitter 118 onto a target portion 120 (e.g., one or more dies)of substrate 114. Projection system 108 can project an image of thearray of individually controllable elements 104 onto substrate 114.Alternatively, projection system 108 can project images of secondarysources for which the elements of the array of individually controllableelements 104 act as shutters. Projection system 108 can also comprise amicro lens array (MLA) to form the secondary sources and to projectmicrospots onto substrate 114.

Source 112 (e.g., an excimer laser, or the like) produces abeam ofradiation 122. Beam 122 is fed into an illumination system (illuminator)124, either directly or after having traversed conditioning device 126,such as a beam expander 126, for example. Illuminator 124 can comprisean adjusting device 128 that sets the outer and/or inner radial extent(commonly referred to as σ-outer and σ-inner, respectively) of theintensity distribution in beam 122. In addition, illuminator 124 caninclude various other components, such as an integrator 130 and acondenser 132. In this way, beam 110 impinging on the array ofindividually controllable elements 104 has a desired uniformity andintensity distribution in its cross-section.

In one example, source 112 is within the housing of lithographicprojection apparatus 100 (as is often the case when source 112 is amercury lamp, for example). In another example, source 112 is remotelylocated with respect to lithographic projection apparatus 100. In thislatter example, radiation beam 122 is directed into apparatus 100 (e.g.,with the aid of suitable directing mirrors (not shown)). This latterscenario is often the case when source 112 is an excimer laser. It is tobe appreciated that both of these scenarios are contemplated within thescope of the present invention.

Beam 110 subsequently interacts with the array of individuallycontrollable elements 104 after being directed using beam splitter 118.In the example shown, having been reflected by the array of individuallycontrollable elements 104, beam 110 passes through projection system108, which focuses beam 110 onto a target portion 120 of substrate 114.

With the aid of positioning device 116, and optionally interferometricmeasuring device 134 on a base plate 136 that receives interferometricbeams 138 via beam splitter 140, substrate table 106 is movedaccurately, so as to position different target portions 120 in a path ofbeam 110.

In one example, a positioning device (not shown) for the array ofindividually controllable elements 104 can be used to accurately correctthe position of the array of individually controllable elements 104 withrespect to the path of beam 110, e.g., during a scan.

In one example, movement of substrate table 106 is realized with the aidof a long-stroke module (course positioning) and a short-stroke module(fine positioning), which are not explicitly depicted in FIG. 1. Asimilar system can also be used to position the array of individuallycontrollable elements 104. It will be appreciated that beam 110 mayalternatively/additionally be moveable, while substrate table 106 and/orthe array of individually controllable elements 104 may have a fixedposition to provide the required relative movement.

In another example, substrate table 106 may be fixed, with substrate 114being moveable over substrate table 106. Where this is done, substratetable 106 is provided with a multitude of openings on a flat uppermostsurface. A gas is fed through the openings to provide a gas cushion,which supports substrate 114. This is referred to as an air bearingarrangement. Substrate 114 is moved over substrate table 106 using oneor more actuators (not shown), which accurately position substrate 114with respect to the path of beam 110. In another example, substrate 114is moved over substrate table 106 by selectively starting and stoppingthe passage of gas through the openings.

Although lithography apparatus 100 according to the invention is hereindescribed as being for exposing a resist on a substrate, it will beappreciated that the invention is not limited to this use and apparatus100 may be used to project a patterned beam 110 for use in resistlesslithography, and for other applications.

The depicted apparatus 100 can be used in at least one of four modes:

1. Step mode: the entire pattern on the array of individuallycontrollable elements 104 is projected during a single exposure (i.e., asingle “flash”) onto a target portion 120. Substrate table 106 is thenmoved in the x and/or y directions to a different position for adifferent target portion 120 to be irradiated by patterned beam 110.

2. Scan mode: essentially the same as step mode, except that a giventarget portion 120 is not exposed in a single “flash.” Instead, thearray of individually controllable elements 104 moves in a givendirection (e.g., a “scan direction,” for example, the y direction) witha speed v, so that patterned beam 110 is caused to scan over the arrayof individually controllable elements 104. Concurrently, substrate table106 is simultaneously moved in the same or opposite direction at a speedV=Mv, in which M is the magnification of projection system 108. In thismanner, a relatively large target portion 120 can be exposed, withouthaving to compromise on resolution.

3. Pulse mode: the array of individually controllable elements 104 iskept essentially stationary, and the entire pattern is projected onto atarget portion 120 of substrate 114 using pulsed radiation system 102.Substrate table 106 is moved with an essentially constant speed, suchthat patterned beam 110 scans a line across substrate 106. The patternon the array of individually controllable elements 104 is updated asrequired between pulses of radiation system 102, and the pulses aretimed such that successive target portions 120 are exposed at therequired locations on substrate 114. Consequently, patterned beam 110can scan across substrate 114 to expose the complete pattern for a stripof substrate 114. The process is repeated until complete substrate 114has been exposed line by line.

4. Continuous scan mode: essentially the same as pulse mode except thata substantially constant radiation system 102 is used and the pattern onthe array of individually controllable elements 104 is updated aspatterned beam 110 scans across substrate 114 and exposes it.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Exemplary Elements in the Array of Programmable Elements

FIG. 2 shows a top view of an array of individually controllableelements 204, according to one embodiment of the present invention. Eachelement 242 in array of individually controllable elements 204 includesan active area 244 and an inactive area 246. Active areas 244 can beformed of mirrors, liquid crystal display elements, grating lightvalves, etc., discussed in more detail above, and are used to patternincoming light, while inactive areas 246 include circuitry andmechanical devices and structures. The devices and structures ininactive areas 246 are used to control and/or move (e.g., tilt, piston,etc.) active areas 244 to turn active areas 244 ON and OFF, and in someexamples, to move active areas 244 to and through various intermediatestates.

FIGS. 3 and 4 depict a top and side view, respectively, of an activearea 344 (e.g., reflective device, mirror, etc.) of an element 342 in anarray of controllable elements 204 (FIG. 2), according to one embodimentof the present invention. A mirror 344 includes a first portion 346coupled to a central area 348 of a second portion 350. In thisembodiment, both portions 346 and 350 are reflective portions. Throughthe coupling, first and second steps 352 and 354 are formed. Each step352/354 has a step height (S_(H)) and a step width (S_(W)). In oneexample, mirror 344 is a tilting mirror having λ/4 height steps 352/354(i.e., S_(H)=λ/4). Also, mirror 344 has a mirror width (M_(W)). Mirror344 tilts around rotation around axis 356. As is known in the art,depending on an angle and direction of tilt, light reflecting from steps352 and 354 will undergo a positive or negative phase change, asdiscussed above.

FIG. 8 depicts a side view of an active area 844 (e.g., reflectivedevice, mirror, etc.) of an element 842 in an array of controllableelements 204 (FIG. 2), according to one embodiment of the presentinvention. A mirror 844 includes a first portion 846 coupled to orformed at peripheral areas 847, which is outside a central area 848 of asecond portion 850. Thus, element 842 can be fabricated either byremoving material from central area 848 or adding material to peripheralportions 847. In this embodiment, both portions 846 and 850 arereflective portions. Through the coupling/formation, first and secondsteps 852 and 854 are formed. Each step 852/854 has a step height(S_(H)) and a step width (S_(W)). In one example, mirror 844 is atilting mirror having λ/4 height steps 852/854 (i.e., S_(H)=λ/4). Also,mirror 844 has a mirror width (M_(W)). Mirror 844 tilts around rotationaround axis 856. As is known in the art, depending on an angle anddirection of tilt, light reflecting from steps 852 and 854 will undergoa positive or negative phase change, as discussed above.

It is to be appreciated that elements 342 and 842 will functionsimilarly, thus only element 342 will be described hereinafter. Thefunctionality described below applies equally to element 842, asappropriate.

In various examples, using appropriate step height/width parameters,mirror 344 can emulate Binary masks, attenuating phase-shift mask (AttPSMs) and alternating phase-shift masks (Alt PSMs).

Phase-shifting mask technology refers to a photolithographic mask thatselectively alters the phase of the light passing through certain areasof the mask to improve resolution and depth of focus according toprinciples of destructive interference. For example, in a simpleattenuating phase shifting mask, a layer of material is selectivelylocated to attenuate light passing through it and shift the light 180degrees out of phase from light passing through adjacent areas notcovered by the phase shifting material. This 180 degree phase differencecauses any light overlapping from two adjacent apertures to interferedestructively, thereby reducing the width of the feature at the wafer.This is obtained in maskless lithography through use of control of eachindividually controllable element and/or groups of individuallycontrollable elements to form patterns that patterning impinging lightto achieve these light characteristics.

An attenuating phase shifting mask differs from an alternating phaseshifting mask in that the alternating phase shifting mask generally doesnot have a partially transmitting phase shifting material, but ratherincludes trenches in the mask to shift the phase of transmitted lightadjacent to the features.

Thus, PSMs have transmissive areas that are in or out of phase withrespect to each other. When two transmissive areas are out of phase withrespect to each other, images at an image plane are made sharper. Thus,through appropriate selection of step heights and widths for elements344 when used in array 104 (FIG. 1) or 204 (FIG. 2), for example,emulation of one of these phase shifting masks can be achieved, whichallows for a shaper image to be formed at an image plane (not shown)than conventional mirrors discussed.

In one example, when compared to flat tiling mirrors, mirror 344 canemulate an Alt PSMs with considerably less light loss than the flattilting mirrors described above. For example, 95% loss for the flattilting mirror compared to 64% loss for mirror 344. Also, being able toemulate Att PSMs allows for desirable depth of focus (e.g., an increaseddepth of focus) and exposure latitude characteristics from mirror 344.

In one example, a size of assist features (e.g., features intended toimprove lithography on a wafer, for example, optical proximitycorrection features, serifs, hammerheads, scattering bars,anti-scattering bars, etc.) that can be replicated with mirror 344 isonly limited by the pixel size. In contrast, when using conventionalpiston mirrors a smallest assist feature cannot be less than asuper-pixel size, e.g., at least twice the pixel size.

Also, as compared to a single step mirror described above, since steps352/354 are added on each side of mirror 344, there is no asymmetricdeformation as a result of adding steps 352/354. Also, thicker edges, ascompared to exemplary single step mirrors described above, due todimensions of steps 352/354 should reduce the amount of edge curlingcompared to a single step mirror.

Exemplary Reflectance Characteristics of Dual Phase Step Elements

FIGS. 5 and 6 show graphs 500 and 600 that depict reflectivity over arange of tilt angles for flat mirrors as compared to dual phase stepmirror 344 (FIGS. 3 and 4), according to embodiments of the presentinvention. In each graph, a reflectivity curve 560/660 is a resultproduced using a dual phase step mirror 344. A reflectivity curve562/662 is a result produced using a conventional flat mirror.

In various examples, adjusting the step width of mirror 344 results inmirror reflectivity curve 560/660 to either optimize the ratio ofpositive versus negative amplitude, to extend a tilt range, to changethe pixel state at rest depending on a desired application, or the like.

Flat tilting mirrors can achieve an intensity modulation anywherebetween 100% positive phase intensity and 4.7% negative phase intensity.This is shown in FIGS. 5 and 6 in curves 562 and 662, respectively,which both show a maximum positive intensity of 1 and negative intensityof −2. This limited negative phase intensity has proven to be a majorlimitation in flat tilting mirrors emulating alternating phase shiftingmasks without significant light loss.

In one example, a reflectivity amplitude or graytone associated withtilting mirror 344 (FIGS. 3-4) with two λ/4 high height steps 352/354,where each phase step 352/354 is located at a distance w_(step) (waferscale) away from the nearest mirror edge, is given by:

${A\left( {0,0} \right)} = {{{- \sin}\;{c\left( \frac{2\;\alpha\;{Mw}}{\lambda} \right)}} + {2\left( {1 - {2\frac{w_{step}}{w}}} \right)\sin\;{c\left( {\frac{2\;\alpha\;{Mw}}{\lambda}\left( {1 - {2\frac{w_{step}}{w}}} \right)} \right)}}}$

where M is the demagnification of the optical system, w is the pixelsize on wafer scale (actual mirror width/M), α is the tilt angle, wstepis the step width and λ is the imaging wavelength. The optical pathdifference for a phase step height of λ/4 is λ/2 because the incidentlight beam is reflected off the surface of the mirror 344, and hence thebeam traverses steps 352/354 twice.

FIG. 5 is based on mirror 344 having a pixel size of about 30 nm (mirrorsize at an object (not shown)) and a step width of about 11.8 nm. Inthis example, step widths of steps 352 and 354 are chosen in order toproduce a reflectivity curve 560 with equal positive and negativemaximum amplitudes. The maximum negative amplitude is achieved at zerotilt (about −0.6 amplitude or about −36% intensity), while the maximumpositive amplitude is obtained at about 17 mrad tilt (about 0.6amplitude or about 36% intensity). The reflectivity zero crossing occursat about 7.5 mrad tilt. In this example, mirror 344 can emulate binary,Att PSM, and Alt PSM reticles. The light loss when emulating Alt PSMmasks is very small compared to what would be needed with a flat tiltingmirror, as shown in curve 562.

FIG. 6 is based on mirror 344 having a pixel size of about 30 nm (mirrorsize at an object) and a step width of about 7.5 nm. The intensitymodulation ranges of curve 660 are from about −10% to about +42%,relative to the flat tilting mirror curve 662.

Telecentric Error Correction Using A Dual Phase Step Reflection Device

FIG. 7 shows a graph 700 illustrating a two dimensional diffractionpattern formed from light reflecting from mirror 344 when it is used ina patterning device (e.g., patterning device 104), according toembodiments of the present invention. In one example, a normalized 2Ddiffraction pattern 700 of is given by:

${A\left( {l,m} \right)} = {\sin\;{c(m)}{\quad{\left\lbrack {{{- \sin}\;{c\left( {l - \frac{2\;\alpha\;{Mw}}{\lambda}} \right)}} + {2\left( {1 - {2\frac{w_{step}}{w}}} \right)\sin\;{c\left( {\left( {l - \frac{2\;{\alpha Mw}}{\lambda}} \right)\left( {1 - {2\frac{w_{step}}{w}}} \right)} \right)}}} \right\rbrack{where}\text{:}\mspace{14mu}\begin{matrix}{f_{0} = \frac{1}{w}} \\{f_{x} = {l \cdot f_{0}}} \\{f_{y} = {m \cdot f_{0}}}\end{matrix}}}}$

l and m are normalized spatial frequencies when the amplitude isnormalized to the peak amplitude of the diffraction pattern of thetilting mirror without the phase steps.

In the example shown, dual phase step mirror 344 has about a about 11.8nm step width and is at about zero tilt. In this example, the symmetryof the diffraction pattern with respect to the vertical axis of thegraph 700 shows that a graytone of mirror 344 depends on the magnitudeof the tilt angle, but not a sign of the tilt angle. Thus, correctingfor telecentric errors with mirror 344 can be carried out in the sameway as for the conventional flat tilting mirror. For example, adjacentelements 344 in an array 204 (FIG. 2) have alternating signs (e.g.,positive or negative) of their tilt angles, for instance in acheckerboard fashion. Unlike the piston superpixel or the single phasestep mirror described above, correcting for the telecentric error withmirror 344 will produce no additional burden on a datapath.

In one example, using mirror 344 allows for tilting to be restricted toone direction only, and still result in both negative and positiveamplitudes. This is in contrast to the single step mirror discussedabove, which requires each mirror to tilt in both directions. Thus, inthis example using mirror 344 provides a simple scheme for correctingnon-telecentricity by simply alternating the sign of the tilt angle.

In contrast, as discussed above, to correct for telecentricity errorsusing the single phase step mirror requires alternating the position ofthe phase edge or step (right or left) and the sign of the tilt angle.This results in the dependence of the tilt angle sign on the position ofthe edge. This means that in order to achieve a given graytone with aparticular mirror, the sign of the tilt angle needed will requireknowledge of where the step is located, which creates an additionalstrain on the data path.

CONCLUSION

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.Thus, the breadth and scope of the present invention should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents.

1. A system, comprising: an illumination system that supplies a beam ofradiation; an array of individually controllable elements that patternsthe beam, the array of individually controllable elements comprisingmirrors including a first portion having a first size and a secondportion having a second size, which is smaller than the first size, suchthat the first and second portions are arranged together to producefirst and second steps on opposite edges of each of the mirrors; and aprojection system that projects the patterned beam onto a target portionof an object.
 2. The system of claim 1, wherein a height and a width ofthe first and second steps of each respective one of the mirrors aresized to produce substantially equal positive and negative maximumamplitudes at the target portion over a complete range of tilt angles ofthe mirror.
 3. The system of claim 1, wherein default positions of themirrors are their ON states.
 4. The system of claim 1, wherein defaultpositions of the mirrors are their OFF states.
 5. The system of claim 1,wherein a height and a width of the first and second steps of eachrespective one of the mirrors are sized so that the array ofindividually controllable elements emulates a binary reticle.
 6. Thesystem of claim 1, wherein a height and a width of the first and secondsteps of each respective one of the mirrors are sized so that the arrayof individually controllable elements emulates an attenuating phaseshift reticle.
 7. The system of claim 1, wherein a height and a width ofthe first and second steps of each respective one of the mirrors aresized so that the array of individually controllable elements emulatesan alternating phase shift reticle.
 8. The system of claim 1, wherein aheight of the first and second steps on each respective one of themirrors is approximately λ/4, wherein λ is a wavelength of the beam ofradiation supplied by the illumination system.
 9. The system of claim 1,wherein a width of the first and second steps on each respective one ofthe mirrors is approximately 5 nm to 12 nm.
 10. The system of claim 1,wherein the object is a substrate.
 11. The system of claim 1, whereinthe object is a semiconductor substrate.
 12. The system of claim 1,wherein the object is a flat panel display glass substrate.
 13. Thesystem of claim 1, wherein the object is a projection display.
 14. Thesystem of claim 1, wherein a width of the first and second steps on eachrespective one of the mirrors achieves equal maximum positive andnegative amplitudes.
 15. A method, comprising: patterning a beam ofradiation using an array of individually controllable elements, eachelement in the array including a first portion having a first size and asecond portion having a second size, which is smaller than the firstsize, such that the first and second portions are arranged together toproduce first and second steps on opposite edges of each of the mirrors;and projecting the patterned beam onto a target portion of an object.16. The method of claim 15, wherein the projecting step comprises usinga substrate as the object.
 17. The method of claim 15, wherein theprojecting step comprises using a display device as the object.
 18. Themethod of claim 15, wherein each element produces substantially equalpositive and negative maximum amplitudes of reflected light over acomplete range of tilt angles.
 19. The method of claim 15, furthercomprising emulating a binary reticle using the array of individuallycontrollable elements.
 20. The method of claim 15, further comprisingemulating an attenuating phase shift reticle using the array ofindividually controllable elements.
 21. The method of claim 15, furthercomprising emulating an alternating phase shift reticle using the arrayof individually controllable elements.